1. Field of the Invention
The present invention relates generally to medical devices and, more specifically, to implants.
2. Description of the Relevant Art
Implants may be used in human and/or animals to support and/or secure one or more bones. For example, implants may be used in the spine to support and/or replace damaged tissue between the vertebrae in the spine. Once implanted between two vertebrae, the implant may provide support between the two vertebrae and bone growth may take place around and through the implant to at least partially fuse the two vertebrae for long-term support. Implants may include relatively large rims with solid material that may cover, for example, 50% of the area that interacts with the endplate. The rim may provide a contact area between the implant and the vertebral endplates. Large rims may have several drawbacks. For example, large rims may impede bone growth and reduce the size of the bone column fusing the superior and inferior vertebral bodies. Additionally, large rims preferentially support and regionalize loads, preventing distribution of force and accommodating response. The process of localizing loading also serves to under load other areas of the vertebral bodies, thereby activating regional resorption according to negative microstrain.
Spinal implants may include open channels through the center of the supporting rims in a superior/inferior direction. The open channel design may require members of the implant that separate the rims that interact with the vertebral endplates to absorb the compressive forces between the vertebral endplates. This may increase the pressure on smaller areas of the vertebral endplates and may potentially lead to stress risers in the vertebral endplates. Further, while bone graft material is often used in conjunction with implants to encourage bone growth, the open column design of implants may reduce the likelihood of bone graft material from securing itself to the implant which could result in a bio-mechanical cooperation that is not conducive to promoting good fusion.
Bone graft material may be packed into the implant in a high-pressure state to prevent bone graft material from exiting the implant while being placed between the vertebral endplates. The high-pressure state may also reduce the potential for the bone graft material loosening due to motion between the implant and the vertebral endplates or compressive forces experienced during settling of the implant. In addition, a high-pressure environment may allow the bone graft material to re-model and fuse at greater strength. High-pressure states, however, may be difficult to create and maintain for the bone graft material in an implant. In particular, the lack of attachment of the bulk graft cannot fully accept or integrate the differential loading anticipated in normal kinetic scope.
Various embodiments of implant systems and related apparatus, and methods of operating the same are described herein. In various embodiments, an implant for interfacing with a bone structure includes a web structure, including a space truss, configured to interface with human bone tissue, including cells, matrix, and ionic milieu. The space truss includes two or more planar truss units having a plurality of struts joined at nodes.
In an embodiment, an implant for interfacing with a bone structure includes: a web structure that is formed from a plurality of struts joined at nodes, wherein the web structure is configured to interface with human bone tissue. The diameter and/or length of the struts and/or the density of the web structure are predetermined such that when the web structure is in contact with the bone structure, its matrix, or the cells from which it is derived, at least a portion of the struts create a microstrain, that is transferred to the adherent osteoblasts, bone matrix, or lamellar tissue, of between about 1με and about 5000με, or between about 500με and 2000με, or between about 1000με and about 1500με or to a negative reflection of compression in interval and resonance with loading in both flexion, extension, torque, or combinations thereof. These ranges are optimized to known load-response dynamics, but are meant as guides rather than limitations to the activity and response. The diameter and/or length of the struts is predetermined so that at least a portion of the struts during loading create a change in length of the adherent osteoblasts, bone matrix, or lamellar tissue, of between about 0.05% and about 0.2% or between about 0.1% and about 0.15% causing an osteogenic response. Struts may have a length of between about 1 mm to about 100 mm. The diameter of the strut may be predetermined such that the struts create a change in length of the adhered osteoblasts of between about 0.05% and 0.2% when the web structure is in contact with the bone structure. Alternatively, the diameter of the strut is predetermined such that the strut undergoes a change of length of between about 0.000125% and 0.0005%, or between about 0.00025% and 0.000375%. In some embodiments, at least a portion of the struts are composed of struts having a length of 1 mm to 100 mm and a diameter ranging between 0.250 mm and 5 mm.
In an embodiment, an implant for interfacing with a bone structure includes a web structure that is formed from a plurality of struts joined at nodes, wherein the web structure is configured to interface with human bone tissue. The web structure, in some embodiments, includes a first bone contact surface and a second bone contact surface. A first portion of struts that comprise the space truss have a physical property that is different from a second portion of the struts that comprise the space truss. The first portion of struts that comprise the space truss may have: a deformation strength; a defined length; a diameter; a differential diameter along its length; a density; a porosity; or any combination of these physical properties; that is different from the second portion of the struts that comprise the space truss. In an embodiment, the space truss includes one or more central struts extending from the first bone contact surface to the second bone contact surface, wherein the central struts have a deformation strength that is greater than or less than the surrounding struts. In an embodiment, the space truss comprises one or more longitudinal struts extending parallel to the first bone contact surface and/or the second bone contact surface, wherein the longitudinal struts have a deformation strength that is greater than or less than the surrounding struts. The diameter of the first portion of the struts may be greater than a diameter of the second portion of the struts. The material used to form the first portion of struts may be different from the material used to form the second portion of struts.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims.